Impregnating and bonding agent for textiles

Abstract

Impregnating and bonding agent for textiles, comprising a mixture of a resorcinol-formaldehyde precondensate A, a rubber latex B and a melamine-formaldehyde resin C, impregnating process and reinforced rubber articles produced using the impregnates.

Description

[0001] This invention relates to an impregnating and bonding agent for textiles, especially for reinforcing materials which are vulcanized into rubber.

[0002] Textiles such as cords or fabrics based on rayon, polyamide, polyester, polyvinyl alcohol, glass fiber and aramid fiber which are used as reinforcements for rubber articles are customarily impregnated with latex baths which additionally contain resorcinol-formaldehyde resins. Such baths are known as resorcinol-formaldehyde-latex or RFL dips. Impregnation serves to improve the adhesion promotion between rubber and textile. Thus impregnated textiles have only in the outer edge zone (about {fraction (1/10)}-{fraction (1/30)} of the fiber or cord cross section) an impregnation layer which then promotes rubber adhesion during the vulcanizing operation. The interior of the fiber or cord is free of RFL impregnation, as a result of which the cord or fabric possesses good flexibility and has high fatigue resistance due to the preserved filamentary structure.

[0003] Textiles based on polyester or aramid, which by their chemical nature exhibit little adhesion to rubber, are customarily subjected to two-bath impregnations. The first impregnating step, which is likewise aqueous, is used to apply a small amount of an adhesion promoter such as blocked isocyanates or epoxy resins to the textile structure. This is followed by the impregnation with a resorcinol-formaldehyde latex.

[0004] RFL dips are frequently produced in-house by the processors from the ingredients. Resorcinol and formaldehyde are mixed in an amount-of-substance ratio of 1:1.5 to 1:2; after about 6 hours of storage in an alkaline medium at room temperature, the resin solution formed is added to a latex containing natural rubber (NR), styrene-butadiene rubber (SBR) or vinylpyridine copolymer rubber (VP) or a mixture thereof. After a further 12 to 24 hours of "ripening" at constant temperature, which is indispensable for uniform development of adhesion, the bath thus produced is used for impregnating textiles.

[0005] Simpler handling is offered by precondensed resorcinol-formaldehyde resins, which are formulated together with the rubber latex and aqueous formaldehyde solution to form RFL baths, in that the ripening step can be omitted.

[0006] However, owing to their free formaldehyde content, neither type of bath/dip is acceptable from an occupational hygiene standpoint.

[0007] It is an object of the present invention to provide impregnating agents which lead to similar results for the adhesion between rubber and textile reinforcements but contain little if any free formaldehyde.

[0008] This object is achieved by an impregnating and bonding agent which comprises a mixture of a resorcinol-formaldehyde precondensate, a rubber latex and a melamine-formaldehyde resin.

[0009] The present invention accordingly provides an impregnating and bonding agent for textiles for improving rubber adhesion, comprising a mixture of a resorcinol-formaldehyde precondensate A, a rubber latex B and a melamine-formaldehyde resin C.

[0010] The present invention further provides a process for producing a textile reinforcement having enhanced adhesion to rubber, which comprises said textile reinforcement being treated with an impregnating and bonding agent comprising a mixture of a resorcinol-formaldehyde precondensate A, a rubber latex B and a melamine-formaldehyde resin C and subsequently dried.

[0011] The present invention further provides rubber articles having enhanced adhesion between the textile reinforcement and the rubber, wherein said textile reinforcement has been impregnated with an impregnating and bonding agent comprising a mixture of a resorcinol-formaldehyde precondensate A, a rubber latex B and a melamine-formaldehyde resin C and has been vulcanized with a rubber mixture into a rubber article.

[0012] It is a further advantage of the invention that some of the costly resorcinol precondensate can be replaced by an inexpensive melamine resin. There is no longer any need to handle formaldehyde at all when making up the dips. It has also been determined that, surprisingly, the dips of the present invention have distinctly improved storage or aging stability compared with dips composed of resorcinol precondensates and rubber latex, but not the melamine-formaldehyde resin which is present according to the present invention.

[0013] The impregnating and bonding agent of the present invention is substantially free of formaldehyde. The mass fraction of free formaldehyde in the impregnating and bonding agent is preferably less than 0.5%. The impregnating and bonding agent preferably comprises resorcinol-formaldehyde precondensate A and melamine-formaldehyde resin C in a mass ratio (each based on solid resin) of 9:1 to 1:9, preferably 7:3 to 3:7 and more preferably 4:6 to 6:4. The ratio of the sum total of the masses of the solids of resins A and C to the mass of the solid of the rubber in latex B (solids mass fraction or rubber content about 35 to 45 cg/g) is preferably 1:1.5 to 1:15, more preferably 1:1.7 to 1:10 and especially 1:2 to 1:9.

[0014] The resorcinol-formaldehyde precondensate A contains building blocks derived from formaldehyde and building blocks derived from resorcinol, the amount-of-substance ratio of formaldehyde to resorcinol being 1:1.05 to 1:2, preferably 1:1.2 to 1:1.9 and especially 1:1.5 to 1:1.8. It is essential to maintain a stoichiometric deficiency of formaldehyde; this keeps the resin at low molecular weight and soluble. Optionally, up to 10% of the resorcinol can be replaced by other phenols, preferably dihydric phenols, provided the condensate prepared therefrom remains soluble in water, ie when 1 g of resin is mixed with 100 g of water at room temperature no insoluble residue visible to the naked eye remains.

[0015] The latex B preferably contains a mass fraction of at least 5%, in the solids fraction, of building blocks derived from 2-vinylpyridine. Copolymerized singly or multiply unsaturated comonomers further include, in particular, styrene and butadiene. Latices of rubbers which contain building blocks of vinylpyridine are frequently known together as "vinylpyridine latex". Other monomers customary in rubber chemistry can be used as well, such as methylbutadiene, vinyltoluene, hexadiene and also esters and other derivatives of acrylic acid. According to the invention, it is possible to use mixtures of latices, provided at least one mass fraction of 10% is used of a latex which contains building blocks derived from vinylpyridine. Frequently, blends with natural rubber (NR) latex or styrene-butadiene rubber (SBR) latex are used. In general, however, it is also possible to use natural rubber latex, SBR, CR or NBR latex or suitable blends alone. Suitable latices are also commercially available from tire manufacturers or manufacturers of industrial rubber articles.

[0016] The melamine-formaldehyde resin C is an unetherified condensate of formaldehyde and melamine, the amount-of-substance ratio between the building blocks derived from formaldehyde and melamine in the resin C preferably being between 1.5:1 to 6:1, more preferably between 1.8:1 to 3.8:1 and especially between 2.1:1 and 3.2:1. The resins C are preferably used as an aqueous solution of the pulverulent resins. Resins are referred to as unetherified when not more than 10% of the N-methylol groups are etherified.

[0017] It is also possible for the reinforcements used in the rubber industry, for example fabrics or cords based on cotton, rayon, polyamides (nylon-6, nylon-6,6), polyester (polyethylene terephthalate), aramid (m-phenyleneisophthalamide, p-phenyleneterephthalamide) to be coated with a pre-dip prior to the impregnation with the disclosed impregnating and bonding agent which contains resorcinol resin, pre-dips customarily containing blocked isocyanates or epoxides in the form of aqueous dispersions. The passage through each bath is followed by a thermal treatment (drying or curing). Combinations of epoxides and blocked isocyanates are also effective.

[0018] Textile reinforcements are, if necessary, impregnated with the above-described pre-dip solution by means of a suitable impregnating machine. The cord or fabric tension must here be adjusted such that good penetration of the impregnating solution into the cord or fabric structure is possible. Excess solution is removed by means of stripper devices or suction nozzles after passage through the impregnating bath. After the moist textiles have been dried, they are customarily subjected to a thermal treatment at 130 to 235.degree. C. and preferably at 180 to 220.degree. C., in the course of which the textiles are optionally tensilized.

[0019] The optionally thus pretreated textiles are treated with the above-described resorcinol-formaldehyde rubber latex (RFL) solution or dip in a second actual impregnating step, which can follow immediately after the pretreatment but may also be carried out after an intervening storage period.

[0020] The solids mass fraction of the RFL dip is in the range 10 to 35% and preferably 20 to 30%. The choice of latex to be used should be made according to the solid rubber into which the impregnated textile is vulcanized. After passing through the impregnating bath, the textile is initially dried in a drying zone and subsequently cured at 130 to 235.degree. C. The textile is then wound up and used for manufacturing the envisioned articles.

[0021] Thus impregnated reinforcements can be used for producing V-belts, specifically raw-edge V-belts, transportation belts, hoses, membranes, automotive tires, in particular as a belt material. Cords which have been impregnated as described can further be subsequently processed into "cord fabrics". The rubber articles produced using the thus prepared textiles can subsequently be cut to size, for example V-belts, transportation belts, hoses, membranes.

[0022] The invention will now be more particularly described with reference to examples. Hereinabove and hereinbelow, all % ages are mass fractions (ratio of the mass of the substance in question to the mass of the mixture), unless otherwise stated. Concentrations in "%" are mass fractions of the dissolved substance in the solution (mass of the dissolved substance divided by the mass of the solution).

EXAMPLES

Example 1

Comparative

[0023] A conventional dip is prepared by mixing 200 g of a commercially available vinylpyridine latex (.RTM.Pliocord V 106 S, Goodyear Chemicals), 22.5 g of a resorcinol precondensate (.RTM.Penacolite Resin R 50, 50% solution in water, Indspec Chemical Corporation), 6 ml of 25% aqueous ammonia solution, 9 ml of 39% aqueous formaldehyde solution and 255 ml of completely ion-free water.

Example 2

Inventive

[0024] A dip according to the invention is prepared by mixing 200 g of a commercially available vinylpyridine latex (.RTM.Pliocord V 106 S, Goodyear Chemicals), 11.25 g of a resorcinol precondensate (.RTM.Penacolite Resin R 50, 50% solution in water, Indspec Chemical Corporation), 11.25 g of 50% aqueous solution of an unetherified melamine resin having an amount-of-substance ratio of formaldehyde to melamine of about 2.6:1, 6 ml of 25% aqueous ammonia solution and 255 ml of completely ion-free water.

Example 3

Testing of Adhesion to Aramid Cord; Impregnation with Unaged Dips

[0025] A commercially available aramid cord (.RTM.Twaron, 1680 1 2 Z/S 250, Teijin Twaron BV) was impregnated with a dip as per example 1 and a dip as per example 2. The loading (mass increase due to impregnating agent, based on the mass of the impregnated cord after drying) was about 7.5%. The aramid cord was led through an impregnating tank, excess solution was stripped off and the impregnated cord was dried in a tubular oven at 100.degree. C. in the course of a passage time of 1 minute; curing was carried out directly thereafter in a second tubular oven (residence time 2 minutes, 200.degree. C.)

Example 4

Testing of Adhesion to Aramid Cord; Impregnation with Aged Dips

[0026] Example 3 was repeated except that the two dips were stored at room temperature (20.degree. C.) for 14 days after preparation.

[0027] Adhesion Testing:

[0028] The adhesion test was carried out as a T-test. An impregnated cord was placed between two rubber strips (composition see table 1) of equal thickness and the structure was vulcanized at 145.degree. C. for 45 minutes. Before testing, the test specimens were stored at room temperature for 24 hours. A tensile tester was used to pull the cords out of the composite at an extension rate of 300 mm/min. The results are summarized in table 2. The recipe of the rubber used was:

1TABLE 1 Rubber recipe Mass in g per Ingredients 100 g of rubber Natural rubber (NR) 100 Stearic acid 0.8 .RTM. Vulkanox HS 0.8 (TMQ, 2,2,4-trimethyl-1,2- dihydroquinoline, polymerized) .RTM. Vulkanox 4010 NA 0.6 (IPPD; N-isopropyl-N'-phenyl- p-phenylenediamine) Zinc oxide 7.0 .RTM. Naftolen V 4055 (plasticizer oil) 7.0 Carbon black 43.0 Sulfur 2.8 .RTM. Rhenogran CTP 80 (N- 0.5 cyclohexylthiophthalimide) .RTM. Vulkacit LDA (ZDEC, zinc 0.7 diethyldithiocarbamate)

[0029] The measured result reported is the force per unit length at which yarn pullout was observed.

2TABLE 2 Adhesion to aramid (length-specific pullout force F.sub.L in N/cm) Dip of example 1 2 F.sub.L (unaged) in N/cm 111 109 F.sub.L (aged) in N/cm 89 140

[0030] Whereas a conventional dip (resorcinol precondensate and formaldehyde together with vinylpyridine latex) gave an acceptable adhesion value when freshly prepared, the adhesion value decreases by about 20% to an unacceptable level after this dip has been stored for 14 days. In contrast, the dip according to the present invention, which starts from approximately the same fresh value, improved on storage by about 27% in terms of adhesion performance. The dips according to the present invention can therefore remain in the baths even in the event of disruptions to the production process; the results do not deteriorate as a result. In the case of conventional dips, however, the baths have to be refilled after disruptions to the production process.

Example 5

Testing of Adhesion to Polyester Cord

[0031] Example 3 was repeated except that the aramid cord was replaced by a polyester cord (1670 1 2 Z/S 340, KoSa GmbH & Co. KG). To test the stability in storage, a comparison was arranged as in example 4 between freshly prepared dips (as per examples 1 and 2) and dips which, before the impregnating operation, were stored at room temperature for 14 days after preparation.

[0032] The predrying was carried out as above at 100.degree. C. for 1 minute, and the curing was carried out at 230.degree. C. for 70 seconds. The results of the adhesion test, which was carried out as described above, are summarized in table 3.

3TABLE 3 Adhesion to polyester (length-specific pullout force F.sub.L in N/cm) Dip of example 1 2 F.sub.L (unaged) in N/cm 165 160 F.sub.L (aged) in N/cm 126 153

[0033] There is no improvement in adhesion on storage, but, within the margin of error, the adhesion provided by the dip according to the present invention remains virtually unchanged (-4%), while in the case of the conventional dip (example 1) the adhesion decreases by about 24% after storage.

Example 6

Testing of Aging at Elevated Temperature

[0034] The dip of example 2 according to the present invention was used to carry out further aging tests. The following adhesion values on polyester cord (as in example 5) were determined for the storage conditions specified in table 4:

4TABLE 4 Adhesion to polyester (length-sp cific pullout force F.sub.L in N/cm) Storage F.sub.L in N/cm directly after preparation 160 9 hours; 50.degree. C. 166 18 hours; 50.degree. C. 162 14 days; room temperature (20.degree. C.) 153 9 hours; 50.degree. C. + 14 days; 20.degree. C. 142 18 hours; 50.degree. C. + 14 days; 20.degree. C. 140

[0035] It was found that the system according to the present invention provides advantages even on storage at comparatively high temperatures.

Claims

What is claimed is:

1. An impregnating and bonding agent for textiles, comprising a mixture of a resorcinol-formaldehyde precondensate A, a rubber latex B and a melamine-formaldehyde resin C.

2. An impregnating and bonding agent for textiles as is claimed in claim 1, wherein said resorcinol-formaldehyde precondensate A and said melamine-formaldehyde resin C are present in a mass ratio (each based on solid resin) of 9:1 to 1:9.

3. An impregnating and bonding agent for textiles as is claimed in claim 1, wherein the ratio of the sum total of the masses (solids fraction in each case) of said resins A and C to the mass of said rubber (solids fraction) in said latex B is 1:1.5 to 1:15.

4. An impregnating and bonding agent for textiles as is claimed in claim 1, wherein the amount-of-substance ratio in said resorcinol-formaldehyde precondensate A of the building blocks derived from formaldehyde and the building blocks derived from resorcinol is 1:1.05 to 1:2.

5. An impregnating and bonding agent for textiles as is claimed in claim 1, wherein the amount-of-substance ratio in said melamine-formaldehyde resin C between the building blocks derived from formaldehyde and from melamine is between 1.5:1 to 6:1.

6. An impregnating and bonding agent for textiles as is claimed in claim 1, wherein said latex B contains a mass fraction of at least 5%, in the solids fraction, of building blocks derived from 2-vinylpyridine.

7. An impregnating and bonding agent for textiles as is claimed in claim 1, wherein said latex B is a mixture of latices, at least one mass fraction of 10% being present of a latex which contains building blocks derived from vinylpyridine.

8. A process for producing a textile reinforcement having enhanced adhesion to rubber, which comprises said textile reinforcement being treated with an impregnating and bonding agent as claimed in claim 1 and subsequently dried.

9. A rubber article having enhanced adhesion between a textile reinforcement and said rubber, wherein said textile reinforcement has been impregnated with an impregnating and bonding agent comprising a mixture of a resorcinol-formaldehyde precondensate A, a rubber latex B and a melamine-formaldehyde resin C and has been vulcanized with a rubber mixture into a rubber article.